1. Field of the Invention
The present invention relates to a camera and an accessory, such as an interchangeable lens or the like, arranged to be capable of communicating with each other.
2. Description of Related Art
In a conventional camera system composed of a camera body and an accessory, mounted on the camera body, arranged to be capable of communicating with each other, a maximum amount of electric power to be supplied from the camera body to the accessory is determined beforehand, and the accessory is made to operate within the limit of such a maximum amount of electric power. This limit is set for the purpose of saving operations to be performed on the side of the camera body from being affected by the operation of the accessory even when the remaining amount of electric energy of a battery mounted on the camera body is small. An example of this arrangement was disclosed in Japanese Laid-Open Patent Application No. HEI 7-194153, in which the accessory is a lens having a built-in vibration wave motor for lens driving.
As for the conventional communication between a camera body and an accessory in the camera system, a single communication method only is employed, for example, as disclosed in Japanese Laid-Open Patent Application No. HEI 6-3582.
As mentioned above, in the conventional camera system, the maximum amount of electric power to be supplied from the camera body to the accessory is determined beforehand. The accessory is, therefore, allowed to operate only within the predetermined limit of electric power even when the power supply battery of the camera body still has a sufficiently large margin in suppliable electric energy. This has presented the following problems.
In a case where the accessory included in a camera system is an interchangeable lens, for example, it is sometimes necessary to move a focusing lens at a faster speed than an ordinary speed in an automatic focusing operation or the like. However, since the focusing lens is arranged to operate only within the limit of the predetermined amount of electric power even when a larger amount of electric energy is available from the power supply battery disposed within the camera body, it has been impossible to carry out a computing operation and other processes at a higher speed by increasing power consumption at a control circuit or to increase a focusing lens driving force by increasing power consumption at a driving circuit. The conventional arrangement thus has been incapable of meeting such a requirement.
Further, the method of the conventional camera systems for communication between a camera body and an accessory has been developed only for the conventional camera systems. Their communication statement is thus arranged also only for the conventional camera systems and is hardly applicable to a system wherein a camera body is arranged to have a new function of designating an electric power to be supplied to an accessory. Therefore, in a case where any special data is required for a new function, the communication becomes impossible, because no instruction can be issued for the special data.
Further, such special data may be communicated by changing the conventional communication method. However, the camera system then might malfunction if the camera system includes the conventional accessory which is not arranged for processing the new communication statement.